Conventionally, an injection valve is used for a crawler tension adjustment mechanism for adjusting the tension of a crawler running apparatus of a crawler-type vehicle, for example a hydraulic shovel. The injection valve includes a valve body having a flow path through which an incompressible fluid such as grease flows to a sealed chamber in a cylinder body. During injection of this incompressible fluid, a spherical check valve that is provided in the middle of the flow path of the valve body prevents the backflow of the incompressible fluid, and a foreign matter intrusion prevention valve is provided at the upstream side of this check valve. See Japanese Unexamined Patent Application Publication No. 2010-215207 and Publication No. 2012-233538 for examples. In this configuration however, there is a concern that a failure of the check valve allows the incompressible fluid to backflow in the flow path at high pressure and damage the foreign matter intrusion prevention valve.
A configuration is illustrated is in Japanese Unexamined Patent Application Publication No. 2012-148592 in which a groove is provided at an attachment screw on the outer side of an injection valve to thereby allow fluid to escape from the downstream side. In the case of this configuration however, the pressure cannot escape unless the injection valve is first loosened.